The present invention relates to the preparation of an o-naphthoquinonediazide sulfonic acid ester. More particularly, it relates to a process for esterifying an o-naphthoquinonediazide sulfonic acid halide, in particular chloride, with a mono- or polyvalent phenolic compound, in a solvent in the presence of a basic component, followed by precipitation of the ester and drying. The invention also relates to the use of the ester in a photosensitive mixture.
German Pat. No. 865,860 (equivalent to U.S. Pat. No. 3,046,120) discloses that photosensitive components, which are suitable as basic materials for copying layers, can be obtained from reaction products of o-naphtho-quinonediazide sulfonic acid halides with alkali-soluble phenol/formaldehyde resins.
In general, the esterification reaction between the o-naphthoquinonediazide sulfonic acid halide and the phenolic compound is conducted in a polar organic solvent, for example, dioxane, acetone, methyl-ethyl ketone, or in a solvent mixture, in a way such that inorganic bases, for example, alkali carbonates, alkali bicarbonates, alkaline-earth carbonates, and the like, are added to the reaction mixture in molar ratios as an acid-binding, basic component.
When the reaction is completed, the reaction products can be isolated from the mixture in various ways, for example, by precipitation with a non-polar solvent or by the addition of water. Due to the process of preparation employed, the resulting products still contain small amounts of the metal ions used for the condensation reaction, and therefore they cannot be used without reservation.
German Auslegungsschrift No. 20 44 868 (equivalent to U.S. Pat. No. 3,647,443) discloses the reaction of o-naphthoquinonediazide sulfonyl chloride with phenolic components in solvents, such as pyridine, picoline, lutidine, or triethylamine. The reaction can be performed under standard conditions and at reduced or elevated temperatures. The reaction products are isolated by neutralizing the reaction mixture with a diluted acid, for example, hydrochloric acid, followed by extraction with the aid of a halogenated hydrocarbon solvent, for example, methylene chloride.
Apart from the use of bases which in some cases present toxic hazards, this process has the disadvantage that a residual portion of alkaline hydrochlorides remains in the reaction product. During the working-up of the reaction products, these residuals may cause discolorations or, in the course of the preparation of photosensitive systems from the products, lead to damage to the sensitive processing equipment by corrosion. Another disadvantage resides in the high technical expenditure which is necessary to remove the remaining alkaline hydrochlorides from the reaction product.
With the increasing scale of integration, the esters of o-naphthoquinonediazide sulfonic acid and the photosensitive positive-working reproduction layers prepared from them, for example, for applications in the field of printed circuit technology and especially for the patterning of silicon surfaces in the field of microelectronics, have to satisfy continuously increasing requirements. In this respect, one of the most stringent requirements is the exclusion of metal ions in the reaction product.
The main requirements concern the absence of ions in the photosensitive mixtures. Particularly disturbing are metal ions, for example, Na, K, Mg, Mn, Fe, Bi, Sb, As, Cu, Cr, Ni, Zn, Se ions, because these either act as so-called doping elements or adversely affect the behavior during the subsequent etching step by causing irregularities in the crystal lattice of the silicon surface.